Recently, as portable electronic instruments, such as portable computers, portable phones and camcorders, have been steadily developed so that they are downsized and lightened, lithium secondary batteries used as drive sources for the electronic instruments are also required to have compact size and light weight.
A lithium secondary battery includes a cathode, an anode and an electrolyte. Upon the first charge cycle, lithium ions are deintercalated from a cathode active material. Then, the lithium ions are intercalated into an anode active material, such as carbon particles, and are deintercalated from the anode active material upon discharge. In this manner, lithium ions transfer energy while they reciprocate between the cathode and the anode, thereby allowing the battery to be charged/discharged.
In general, an electrode for a lithium secondary battery is obtained by dissolving an electrode active material, a conductive agent, a binder, etc. into a dispersion medium to form an electrode slurry, and by applying the electrode slurry onto a current collector, followed by drying and pressing. Binders that are used conventionally are broadly classified into polyvinylidene difluoride (PVdF)-based binders and styrene-butadiene rubber (SBR)-based binders. Among these binders, polyvinylidene difluoride-based binders require the use on an non-aqueous toxic solvent, for example, N-methylpyrrolidone (NMP), as a dispersion medium for an electrode slurry, thereby potentially causing environmental pollution. Additionally, such binders may cause degradation of the quality of a battery, when the dispersion medium is not completely removed from the electrode slurry after applying the electrode slurry onto a current collector. Thus, an additional step for removing the dispersion medium is essentially required. Also, even after an electrode is finished, a polar electrolyte cannot infiltrate into electrode active material particles with ease to thus cause an increase in interfacial resistance in the electrode and an increase in internal resistance of a battery, resulting in degradation of the quality of the battery. Further, a long period of time and complicated processing conditions are required in order to allow a polar electrolyte to infiltrate into an electrode so that the electrode is wetted with the electrolyte. Under these circumstances, smooth lithium ion conduction cannot be made, resulting in degradation of the quality of a battery.